1. Field of the Invention
This invention relates to phenol/aldehyde-based polyols and to rigid cellular compositions derived from these polyols. Specifically it deals with modified benzylic ether-containing resole polyols and the rapid curing, low combustibility, low friability, closed cell, rigid cellular plastic compositions obtained by reaction of the polyols with polyisocyanates.
2. Description of the Prior Art
Simple phenolic foams obtained by the thermal and acid catalyzed polymerization of resole resins or of novolac resins with added aldehydic compounds are old in the art. Such foams are noted particularly for their excellent fire resistance. However, they also possess the properties of punking, extreme friability, and being opened-cell which make them ill-suited for insulation or any use where the foam must be handled or support weight. There is a long-established desire to use such phenolic resins in cellular polyurethane or polyisocyanurate formations with the hope of improving strength, insulation, and punking properties while retaining the inherent low combustibility of phenolic foams.
In the art of phenol/aldehyde condensates, it is known that the properties and structures of the products vary, primarily dependent on the phenol/aldehyde mole ratio and the type of catalysis used for the condensation. Alkaline catalysis (alkaline hydroxide, organic amines) with aldehyde in excess results in products known as "resoles" having the following idealized formula: ##STR1## where X is H or --CH.sub.2 OH and n=0, 1, 2, 3, or higher.
The hydroxymethyl ring substituents of the above "resole" are highly reactive toward unsubstituted ortho or para phenolic ring positions. Thus, such condensates can be easily cross-linked to form infusible solids by heating or acidifying. Acid catalysis is not normally used in the preparation of resoles since cross-linking leading to gelation can easily occur.
When the phenol is used in molar excess, the product has little or no hydroxymethyl substitution as shown in the following idealized formula: ##STR2## where X is hydrogen and n=0, 1, 2, 3, or higher.
Such products are called "novolacs" and, lacking the reactive hydroxymethyl substituent, can be prepared under acid catalysis to benefit from a faster rate of formation. In all phenol/aldehyde condensates (novolacs and resoles) small quantities of starting materials and intermediates are present.
A British study (Fraser, et al, J. Appl. Chem. 7 689 (1957) showed that electropositive divalent metal ions which also catalyze the phenol/aldehyde condensation, cause (1) the substitution on the phenol ring to occur predominantly in the ortho rather than the para position and (2) results in the formation of a high percentage of benzylic ether linkage in addition to some methylene linkages between phenol rings. This is illustrated in the following formula: ##STR3## where R is --CH.sub.2 OCH.sub.2 --or a mixture of --CH.sub.2 --OCH.sub.2 -- and --CH.sub.2 --
X is H PA1 y is H or --CH.sub.2 OH and PA1 n=1, 2, 3, or higher. PA1 x is H, halogen, C.sub.1 -C.sub.12 alkyl or a mixture thereof; PA1 y is a mixture of hydrogen and -CH.sub.2 OA; PA1 A is a mixture of hydrogen and a radical or mixture of radicals resulting from removal of a hydroxyl group from an aliphatic hydroxyl compound or mixture of compounds having 1 to 4 hydroxyl groups, 1 to 12 carbon atoms and 0 to 5 ether oxygen atoms; PA1 R is --CH.sub.2 OCH.sub.2 -- or a mixture of --CH.sub.2 OCH.sub.2 -- and --CH.sub.2 -- with the ratio of 13 CH.sub.2`OCH.sub.2 -- groups to --CH.sub.2 -- groups being greater than 1; and wherein the amount of substituent radical A is at least 5 mole percent but less than 35 mole percent of the phenol rings present.
The differences between these three types of phenol/aldehyde condensates is demonstrated in their conversion to highly cross-linked infusible phenolic polymers. Resoles, containing an abundance of reactive hydroxymethyl groups and available unsubstituted ring positions, react when heated alone. Novolac, having no significant amount of hydroxymethyl groups, must be heated with an aldehyde source (hexamethylene tetraamine or paraformaldehyde) to undergo cross-linking reaction. The benzylic ether-containing resin will cross-link at a slow rate as the benzylic ether linkage decomposes (at 150.degree. C. and higher temperature) to form methylene bridges and liberate formaldehyde which serves to cross-link the resin. Thus, the stuructural differences between novolacs, resoles, and benzyl ether-containing resins are reflected in and explain the known differences in chemical behavior of these different phenol/aldehyde condensates.
The use of benzylic ether-containing resins in the preparation of polyurethanes has been disclosed in Japanese Pat. No. 1973-43,097 (to Hatashi Chemical Industries) and U.S. Pat. 3,948,824 (to Robins). The benzylic ether resoles use by Robins were prepared according to U.S. Pat. No. 3,485,797. While these patents represented novel improvements over the then existing art, the polyurethane foams obtained by the teaching of these patents have been found both in our laboratories and by others to be deficient in one or more properties (see Example 2 hereinafter; U.S. Pat. No. 4,293,658; and Schafer, et al, J. Cellular Plastics 1978 p. 147). The polyurethane foams obtained were slow to cure and friable. To achieve desirable strength and friability properties required post-curing of the foams at elevated temperatures.
In Great Britain No. 2,033,413, modified resoles are etherified with aliphatic polyols (under acid conditions) and the products are used to prepare polyurethane or polyisocyanurate foams. However, these phenol-formaldehyde derived resins yielded polyurethanes with poor inherent flammability properties. To obtain suitable flame retardant foams required the use of chlorophenol as the phenolic reactant and/or added phosphate-type flame retardant in the foam formulation.
A seemingly related group of patents have recently issued to Vasishth et al and been assigned to Cor Tech Research Ltd. (U.S. Pat. Nos. 4,235,989; 4,219,634; 4,184,032; 4,140,845). Although the patents disclose and teach the preparation of benzyl ether-containing resins in the presence of methanol, the processes and products differ from the present invention in several important respects. The patents teach the use of aqueous formaldehyde plus added water such that the condensation is carried out in an aqueous system until the resin precipitates as a second phase. Second, the reaction is carried out at a lower temperature, from 90.degree. C. to "approximately 100.degree. C." (reflux). Finally, infrared and NMR spectroscopy reported in the patents did not reveal any "reacted" methanol and the resins were not used as "polyols" in polyurethane formation.